Pressure wave propagation induced by short circuits inside power transformers: Development of a simulation tool, comparisons with experiments and applications

Abstract

Transformer explosion and its prevention is a complex industrial issuewhere various physical phenomena occur. To understand them, anexperimental test campaign was performed by CEPEL on large scaletransformers. It consisted in creating arcing in oil filled transformer tanks.The tests confirmed that the arc generates dynamic pressure waves thatpropagate in the oil. Reflections of these waves on the walls build up highstatic pressure to which transformer tanks can not withstand. This staticpressure increase can be prevented by a quick oil evacuation triggered bythe first dynamic pressure peak generated by the electrical arc. Moreover,a numerical tool was developed to simulate the phenomena highlightedduring the tests and mainly the pressure wave propagation. It is thus basedon a compressible two-phase flow modelling where viscous flow,electromagnetic, thermal and gravity effects are taken into account. Theequations are solved using a finite volume method allowing computingcomplex 3D transformer geometries. Comparisons between the dataobtained during the experiments and the results given by the simulationsvalidated the model. It can be used to study transformer explosions as wellas depressurisation induced by the explosion prevention technology basedon a quick oil evacuation.